1. Field of the Invention
This invention pertains to an improved method for reducing the olefin content of cracked gasolines without the reduction of octane which is inherent in the prior art (hydrogenation) methods. This invention also pertains to extension of scarce petroleum supplies by utilization of methanol as a component in a gasoline blend and to stabilization of gasoline-methanol mixtures against phase separation at low temperatures or in the presence of water contaminent.
2. Description of Prior Art
In order to produce gasoline and other fine products, the modern refiner is forced to operate under an ever-growing series of constraints. Gasoline product specifications, for example, are now set by government. One important specification involves the bromine number of the final gasoline product, which is a measure of the olefin content of the product.
Since unburned olefins emitted from automobile exhausts interact in the atmosphere with ozone and NO.sub.x to produce smog forming components, it is ecologically desirable to reduce the olefin content of gasoline in order to reduce the amounts emitted as unburned hydrocarbons and, ultimately, smog. Gasolines marketed in California, for example, must have a bromine number of less than 30, which translates to an olefin content of approximately 10 wt %. A typical gasoline from a cracking unit, such as Fluid Catalytic Cracking (FCC) or Thermofor Catalytic Cracking (TCC), however, may have an olefin content of 20 wt % or more. Thus, to meet the prescribed product specifications, the refiner must hydrogenate a large quantity of the olefins present in cracked gasoline. Besides being very expensive, hydrogenation of olefins presents another major problem to the refiner since such hydrogenation generally causes the gasoline product to lose from about 2 to 10 Research Octane Numbers. This loss of octane is due to conversion of higher octane olefinic components to lower octane paraffinic components.
In addition to the constraints described above, the modern refiner is also faced with a decreasing availability of desirable crudes. As the amounts of these desirable crudes decreases, the refiner will be forced to use crudes of much poorer quality. Therefore, it will become more and more difficult to produce desired quantities of gasoline which meet the prescribed product specifications. For example, if the refiner is forced to utilize a heavier crude, more gasoline must be produced by catalytic cracking. Such gasoline would have a high olefinic content and would not, without further treatment, meet the bromine number specifications discussed hereinabove.
In order to produce sufficient quantities of gasoline, the refiner must begin to look to non-conventional feedstocks. One such feedstock is alcohol, particularly methanol, which can be produced from abundant coal supplies with existing technology. Indeed, gasolines containing variable amounts of methanol, often 5 to 20 volume percent, have heretofore been proposed as a potentially economical technique for extending gasoline supplies.
The use of gasoline-methanol mixtures, however, has been accompanied by at least two major disadvantages. First, a 10 percent solution of methanol in some gasolines is soluble at room temperature, but separates at low temperatures because of decreased solubility. This problem becomes even more acute when methanol is blended with a gasoline in which the olefins have been hydrogenated to paraffins because methanol is even less soluble in paraffinic stocks than in aromatic or olefinic stocks. Also, the presence of small amounts of water, say 0.1 to 1%, can effect phase separation causing removal of some of the methanol from the gasoline into the water phase.
It has heretofore been reported that certain additive materials, e.g. isobutanol at 2.4% added to a mixture of 10% methanol in gasoline, will maintain the methanol in solution at low temperatures and possibly improve the water tolerance. The principal problem with such approach has been the cost and availability of the additive materials.
The following U.S. patents disclose alcohol-gasoline fuel in which large percentages of petroleum products are avoided. U.S. Pat. No. 1,527,504 shows a fuel with 40-60% methanol, the remainder being benzol and gasoline. In U.S. Pat. No. 1,516,907, the fuel contains 40-70% methanol, the remainder being gasoline. Finally, U.S. Pat. No. 1,474,135 shows a fuel with 25-50% butyl alcohol, the remainder being gasoline. The disclosure of fuels having major proportions of alcohols and smaller amounts of petroleum derived products is contrary to present invention which relates to the use of minor amounts of alcohols to extend gasoline supplies. None of the above patents discloses the components nor the proportions employed in the present invention.
In U.S. Pat. No. 2,087,582, there is disclosed a three component fuel blend consisting of gasoline, alcohol and a metallic-organic anti-knock agent. Again, this patent does not show nor suggest the invention described and claimed herein.
U.S. Pat. No. 3,455,664 teaches that isopropyl alcohol can be produced by hydration of propylene and added to a motor fuel by an extraction process. This patent does not teach hydration of olefinic gasoline nor fuel mixtures of gasoline, methanol and alcohols produced from hydration of olefinic gasoline.
U.S. Pat. No. 3,705,912 merely teaches treating an olefinic component with water in the presence of specific catalysts to produce the corresponding alcohol.